In hydrocarbon producing wells, it is generally necessary to assist the fluids to reach the surface. In some wells, primarily gas producing wells (i.e. wells in formations that produce a high concentration of gas-phase hydrocarbons), one system used to assist production involves the use of a plunger, which acts as a piston to lift accumulated liquids. The plunger is moved upward by gas pressure below the plunger, and then returns downhole once pressure is reduced.
In order to allow the plunger to fall after being lifted to surface, the engagement between the plunger and the inner surface of the production tubing cannot be too strong. At the same time, the engagement must be able to create a sufficient pressure differential across the plunger in order to provide the necessary lift to the plunger. U.S. Pat. No. 8,869,902 (Smith et al.) and U.S. Pat. No. 7,448,442 (Wells) each describe plungers with wear pads carried by a plunger. Downhole pressure enters behind the wear pads to bias them outwards to improve the sealing of the plunger assembly.